The present invention relates to a closing cover for a metal container composed of a body having a substantially cylindrical or other shape, of a closing base crimped onto the lower edge of said body, comprising an interior ring crimped onto the upper edge of the body, with the free side of the ring being shaped so as to have a circumferential groove whose interior wing is reinforced by an rim which is folded back internally or externally in its extension, and a round cover whose marginal part has a convex angular profile with a complementary shape to that of said groove, so as to be held under pressure, and a peripheral reinforcing rim.
Its principal application is in paint and varnish shops as a packing element for pain products containing ingredients which are likely to attack the tin plate at places which are weakened through stamping.
The use for packing and shipping paint products of metal containers provided with a closing cover has been widespread for many years.
The metal containers are generally composed of a metal body having any shape whatever and of a round base crimped onto the lower edge of said body, so a to form the base of said metal container.
The closing cover comprises a metal ring which is stamped to have a profile with a groove and crimped onto the upper edge of the body of said container and a round cover whose marginal part has a circumferential rib which is intended to fit into said groove and provide a sealed metal-to-metal contact on the sides of the groove.
The object of the presence of metal ring is also to reinforce the crush resistance. It provides the closing cover with sufficient rigidity to allow the stacking of many metal containers on top of one another to enable, for example, their being handled on a palette.
In addition, the cover enables the introduction of a screwdriver head between the reinforcing flange and the crimped edge of the ring in order to carry out the removal of the cover without damaging or deforming said cover.
The ring and the cover are profiled such that the peripheral flange of the cover is flush with the crimped edge of the ring in the closed position of the container.
In order to reinforce the rigidity of the ring and improve the degree of sealing and the viability of the closing cover, it is provided to extend the interior wing of the groove of the ring with an interior or exterior folded-back edge coil.
The pressing down of the interior or exterior coil of the metal ring by stamping subjects said coil to extremely severe solicitations. Consequently, crackles are noted in the tin plate sheet which are due to the drawing of the sheets in stamping presses. As these are sheets which are possibly coated with a layer of varnish, it is not surprising to note that, at certain critical points of the folded back edge, the metal ring lacks protection and is directly submitted to the corrosive action of air, water and the solvents contained in the paint, varnish or other liquid or solid compositions packed in said metal containers.
It has therefore been observed that in the known metal containers, with American or triple-tight closures, a risk of rust along the folded back edge occurs during prolonged periods of stocking.
In the metal containers with an interior coil, that is comprising an interior ring whose rim is folded back towards the interior of the container, the annular fold of the free edge of the groove has a circumferential interstice which is in contact with the interior volume of the container, even in the presence of the cover. The formation of rust inevitably causes the contamination of the paint product contained in said container.
In the case of an externally coiled rim composed of a fold towards the interior of the groove, the rust which starts to form from the cutting edge, which is crackled, of the folded back rim extends progressively along the rim to form an annular mass of rust against the contact line of the cover and the interior ring. When the cover is removed, the contents of the metal container are inevitably contaminated.
To overcome this German patent DE-PS No. 687.540 describes a closure for tin plate containers cover internally with a protective film which is held in place by an annular metal closure ring crimped onto the upper edge of the body of the container.
The sealing of the closure is improved by providing an annular joint in the peripheral fold of the cover.
The manufacture of a container provided with such a closure is difficult, due to the fact that the crimping of the annular metal closure ring onto the body of the container and the fixing of the protective film on the coiled end of the ring are relatively laborious.
European patent application No. EP 0002337 also describes a container with a closing cover in which the cover is provided with a groove into which the body of another container can fit, so as to enable stacking and to facilitate packing during stocking and shipping.
The upper rim of the body of the container is provided with a closing annular ring made either of metal or of a resiliently deformable synthetic material. Such a container is, however, subject to corrosion when the metal closing ring is not protected with a protective sheath or has too low shock resistance when the ring consists simply of an annular profile in a synthetic material.
The problem posed consists of fixing, through crimping, a closing ring, which is not subject to corrosion, to the upper rim of the body of a metal container.